Bonding washer

ABSTRACT

A bonding washer for making electrical connection between two metal pieces that are to be mechanically fastened together. The washer, to be interposed between the two metal pieces, may be constructed so as to fasten to one of the pieces before the two pieces are joined. Teeth on the washer, positioned at right angles to the plane of the washer, are forced into each of the two metal pieces when the fastener is tightened, making electrical connection between the two metal pieces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 13/324,688,filed Dec. 13, 2011, which is a continuation of application Ser. No.11/308,683, filed Apr. 21, 2006 (now U.S. Pat. No. 8,092,129), both ofwhich are incorporated by reference herein in the entirety.

FEDERALLY SPONSORED RESEARCH

Not Applicable

REFERENCE TO SEQUENCE LISTING

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to construction of photovoltaic arrays and otherapparatus requiring electrical connection between metal parts.

2. Prior Art

This invention has been devised for use in installing a photovoltaicarray composed of a number of photovoltaic modules that are assembledonto a larger mounting structure. The frames of the individualphotovoltaic modules and the structural pieces on which the modulesmount are generally made out of aluminum. The aluminum is anodized toresist corrosion. As in any source of electrical power, to ensure safetythe metal pieces must be bonded together. Bonded is used here in thetechnical sense to mean permanently joined to form an electricallyconductive path that ensures electrical continuity and has the capacityto safely conduct any current likely to be imposed. Although the framesof the modules are directly bolted or clamped to the mounting pieces,the anodizing insulates the pieces so that they are not electricallyconnected together.

A common practice in the industry is to install a separate grounding lugon each piece that is anodized. The grounding lug is attached to thesheet metal frame of the modules with a thread forming stainless steelscrew. Since the screw cuts into the aluminum it forms an air-tightconnection which will maintain good electrical connection over time. Acommon sheet metal thickness is 0.080 inch and a common screw size is10-32 so that the screw therefore only makes connection on about 2½threads. This gives a marginally acceptable surface contact area interms of mechanical strength and electrical conductivity. It would bedesirable to have a design where the electrical contact area can be mademuch larger.

The stainless steel screw contacts a star washer which in turn contactsthe grounding lug body. The grounding lug accepts a copper wire which isforced to contact the grounding lug by a stainless steel set screw.There are thus four connection points which must be made, sheet metal toscrew, screw to star washer, star washer to lug, and lug to copper wire.It would be desirable to have a design where there are only twoelectrical connection points.

Copper wire is strung between grounding lugs on all the metal pieces andeventually to a ground electrode. The grounding lugs themselves areexpensive and time consuming to install and the wiring adds bothmaterial and labor cost which increase the price of the overall system.It would be preferable if the electrical connection was made directlybetween the metal pieces when they are assembled together.

Star washers, such as that in FIG. 1, are generally available for makingelectrical connections. They are constructed so that they can be punchedand formed out of flat metal stock. The forming process makes a numberof internal or external teeth that are usually twisted so that theyextend above and below the plane of the washer body. Star washers makeelectrical connection to an adjacent piece because they tend to dig into the adjacent piece as they are rotated and compressed by a nut andbolt being tightened. In the intended application, they would beinserted in between the two pieces of metal to be bonded. They willtherefore be separated from the nut and bolt by a layer of material andso will not rotate in the usual manner and therefore will be lesseffective. Star washers are intended for applications where all theyhave to break through is grease or dirt on a metal surface, but anodizedaluminum is a very hard material. The teeth of a star washer will actlike springs and deform back to a flat surface when compressed. This isdesirable for most applications because the spring action maintainscontact. In this application, however, depending on the thickness of theanodizing, the star washer may or may not penetrate the anodizing tomake connection with the underlying aluminum metal. Some examples ofthis type construction are found in U.S. Pat. No. 5,453,027 (Buell etal., 1995),U.S. Pat. No. 5,620,290 (Homfeldt et al., 1997), and U.S.Pat. No. 6,939,097 (Carr et al., 2005), Shapes other than washers mayalso use these twisted type teeth, as in the clips of U.S. Pat. No.4,406,505 (Avramovich 1983) and No. 4,961,712 (Schwenk et al., 1990).

One might consider using a washer so thick that the teeth are unable tospring back to the flat condition; however, such a piece would noteasily fit in between two metal pieces and may cause the two metalpieces to deform. Also since a thick washer requires more material, itwould be more expensive.

A better washer would be constructed so that the teeth are at rightangles to the metal pieces to which contact should be made. Then, whenthe washer is tightened against the metal pieces, the teeth will not beable to spring back into the plane of the washer and will be forced toembed themselves into the adjacent piece. In embedding, both the teethand the metal piece being contacted will deform together, resulting in acontact area where air is excluded so that the contact area will not besubject to corrosion. The height of the teeth can be designed so thatthe washer is guaranteed to punch through a specified thickness ofanodizing. The shape and number of teeth can be designed to give adesired contact area and therefore a desired electrical resistance. Thecontact could be made along the inner diameter of a hole in the metalpieces; however, that might limit the amount of contact area availableso it would be preferable to contact the metal pieces on an exposedface.

The washer of U.S. Pat. No. 5,828,008 (Lockwood et al., 1998) does haveteeth at right angles to the piece to be contacted; however, they areonly on one face. For use with machine screws, two of these washers arerequired. In that case, the conduction path is from the first metalpiece to be connected, to the first washer, then to the machine screw,then to the second washer, then to the second metal piece to beconnected. Since the conduction path has four places where currenttransitions between parts, there is great likelihood of a poorconnection at one of the transition points and hence poor reliability.In addition, the total connection path is much longer than necessary andtherefore will have relatively high resistance. A final problem is thatthe screw must generally be made of stainless steel to resist corrosion.The relatively poor electrical conductivity of stainless steel and thelong path through the screw will limit the amount of current which canbe safely conducted.

In the case of Lockwood, the washer is constructed with a concave shape.As the fastener is tightened, the washer will flatten. This change inshape will give a radial motion to the teeth which will scrape acrossthe metal surface. For anodized surfaces the scraping may not be enoughto break through the coating. It would be preferable to have the teethdirectly penetrate some distance into the metal.

U.S. Pat. No. 5,435,746 (Leeb 1995) and associated U.S. Pat. No.5,501,008 (1996) also use an electrical contact at right angles to thepiece to be contacted, but it is intended for use with specializedassembly tooling and an adhesive which makes the connection permanent.In the case of application to solar modules, it is necessary to providefor module repair or replacement and a permanent connection isinappropriate.

One might consider use of the electrical grounding stud as described inU.S. Pat. No. 5,207,588 (Ladouceur et al., 1993), U.S. Pat. No.5,441,147 (1995), and U.S. Pat. No. 5,644,830 (1997). This invention hasa washer with right angle features connected to the washer and anattached stud, and also has right angle features connected to the washerand an attached rivet. The stud might be inserted through a hole in theframe of the solar module, then a nut fastened to the stud to hold it inplace. The rivet could then be used to join to the mounting structure.This is clearly a cumbersome assembly process. In addition, thegrounding stud will be an expensive part to fabricate and sincetypically four connectors are required per solar module, the total costwill be prohibitive.

Another problem with using available washers is that the washer needs tobe inserted in between two metal pieces. When mounting a photovoltaicmodule there are four mounting holes, so one would need to carefullyposition four washers and then align the module to the mounting pieces.This would clearly be very difficult to do. It would be preferable tohave a washer with features which retain it in position.

There are a number of available washers that have features for retainingto a bolt, such as that of U.S. Pat. No. 5,620,290 (Homfeldt et al.,1997), illustrated in FIG. 1. To use such a washer one would positionfour bolts through the holes in the frame of a module and place a washeron each bolt. The module would then be positioned on the mountingstructure, then the module secured in place with four nuts. There areseveral problems here. The first is that the retaining force may not belarge enough, and as the large and cumbersome module is positioned, thebolts may be knocked loose. It would be preferable to retain the washerdirectly to the module or mount, and then insert the bolts after thepieces have been aligned. A second problem is that the available washersare of the star type construction and do not guarantee connection asdetailed previously.

There are several manufacturers who make inserts that are press fit intosheet metal parts and could thus provide the desired retention feature.For the least assembly effort, it would be desirable to construct theelectrical connecting washer as an integral part of such an insert.Since the press fit process will also guarantee electrical connection,only one side of the washer would need to have the electrical connectingfeatures.

For very high volume applications, it would be desirable to integratethe washer into the fastener and therefore eliminate assembly steps.

Accordingly, several objects and advantages of the present inventionare:

-   -   1. to provide a washer which will guarantee electrical        continuity between two metal pieces after they have been        mechanically assembled even if the pieces are made of anodized        aluminum;    -   2. to provide a washer with a large surface contact area for low        electrical resistance;    -   3. to provide a washer which will be retained on one metal piece        so that a second metal piece may be aligned to the first metal        piece for mechanical assembly without disturbing the washer;    -   4. to provide a washer which requires no special tooling but        makes electrical connection during the mechanical assembly        process.    -   5. to provide a washer which can be integrated with a fastener        for minimum assembly time.

Still further objects and advantages will become apparent from aconsideration of the ensuing description and drawings.

BRIEF SUMMARY OF THE INVENTION

The present invention consists of a bonding washer for maintainingelectrical connection in the joining of two metal pieces, constructedwith metal teeth perpendicular to the body of the washer, and may beconstructed so as to fasten to one of the metal pieces before assembly.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a prior art washer with bolt retention features.

FIG. 2 shows an exploded view of an assembly with a prior art washerwith bolt retention features.

FIGS. 3-8 show perpendicular teeth construction details.

FIG. 9 shows the preferred embodiment of the invention.

FIG. 10 shows the preferred embodiment of the invention inserted onto ametal piece.

FIG. 11 shows an exploded view of an assembly with the preferredembodiment.

FIGS. 12-13 show an alternative embodiment of the invention with clipfeature for thin metal pieces.

FIG. 14 shows an alternative embodiment of the invention with clipfeature inserted onto a thin metal piece.

FIG. 15 shows a second alternative embodiment of the invention with clipfeature for thin metal pieces.

FIG. 16 shows a third alternative embodiment of the invention withfinger retention feature for metal rails.

FIG. 17 shows a third alternative embodiment of the invention withfinger retention feature mounted on a metal rail.

FIG. 18 shows a fourth alternative embodiment of the invention withpress fit retention feature.

FIG. 19 shows a fourth alternative embodiment of the invention withpress fit retention feature inserted into a metal piece.

FIG. 20 shows a fifth alternative embodiment of the invention with pinfeatures.

FIG. 21 shows a sixth alternative embodiment of the invention withdiamonds substituted for pins.

FIG. 22 shows a seventh alternative embodiment of the invention withfeatures for electrical connections on the outside of the pieces beingassembled.

FIG. 23 shows a seventh alternative embodiment of the invention withfeatures for electrical connection on the outside of the pieces beingassembled in exploded view.

FIG. 24 shows a seventh alternative embodiment of the invention withfeatures for electrical connections on the outside of the pieces beingassembled after assembly.

FIG. 25 shows an enlarged view of a seventh alternative embodiment ofthe invention with features for electrical connections on the outside ofthe pieces being assembled after assembly.

FIG. 26 shows a eighth alternative embodiment of the invention withintegral threaded nut.

FIG. 27 shows a eighth alternative embodiment of the invention withintegral threaded nut after assembly.

FIG. 28 shows a ninth alternative embodiment of the invention withintegral rivet feature.

FIG. 29 shows a cross-sectional view of a ninth alternative embodimentof the invention with integral rivet feature.

FIG. 30 shows a ninth alternative embodiment of the invention withintegral rivet feature after assembly.

FIG. 31 shows a tenth alternative embodiment of the invention withintegral solar module end clamping features.

FIG. 32 shows an eleventh alternative embodiment of the invention withintegral solar module midpoint clamping features.

FIG. 33 shows a twelfth alternative embodiment of the invention for usewhen only one metal piece has an anodized coating.

FIG. 34 shows the embodiment of FIG. 33 as it is assembled with a metalrail.

REFERENCE NUMERALS IN DRAWINGS

-   -   100—star washer body (prior art)    -   101—longer teeth of star washer (prior art)    -   102—shorter teeth of star washer (prior art)    -   200—screw (prior art)    -   201—upper metal piece (prior art)    -   202—star washer (prior art)    -   203—lower metal piece (prior art)    -   300—single tooth formed by triangular punch    -   400—four teeth formed by square punch    -   500—multiple teeth formed by circular punch    -   600—single circular tooth formed by circular punch    -   700—tooth formed by pin    -   800—tooth formed by two opposed circular teeth    -   900—upward-facing teeth (preferred embodiment)    -   901—upper washer section (preferred embodiment)    -   902—downward-facing teeth (referred embodiment)    -   903—lower washer section (preferred embodiment)    -   904—hinge (preferred embodiment)    -   905—clearance hole (preferred embodiment)    -   906—fingers (preferred embodiment)    -   1000—hole in first metal piece    -   1001—first metal piece    -   1100—bolt    -   1101—flat washer    -   1102—second metal piece    -   1103—hole in second metal piece    -   1104—flat washer    -   1105—split washer    -   1106—nut    -   1200—upward-facing teeth (first alternative embodiment)    -   1201—body (first alternative embodiment)    -   1202—clearance opening (first alternative embodiment)    -   1203—U-shaped bend (first alternative embodiment)    -   1204—tab (first alternative embodiment)    -   1301—downward-facing teeth (first alternative embodiment)    -   1500—upward-facing teeth (second alternative embodiment)    -   1501—first body section (second alternative embodiment)    -   1502—second set of upward-facing teeth (second alternative        embodiment)    -   1503—second body section (second alternative embodiment)    -   1600—upward-facing teeth (third alternative embodiment)    -   1601—downward-facing teeth (third alternative embodiment)    -   1602—spring fingers (third alternative embodiment)    -   1700—metal rail    -   1701—side of metal rail    -   1702—second side of metal rail    -   1800—downward contacting teeth (fourth alternative embodiment)    -   1801—upward-facing teeth (fourth alternative embodiment)    -   1802—tubular section (fourth alternative embodiment)    -   1803—flat portion (fourth alternative embodiment)    -   2000—flat washer section (fifth alternative embodiment)    -   2001—double pointed pin (fifth alternative embodiment)    -   2002—hole retention feature (fifth alternative embodiment)    -   2100—adhesive layer (sixth alternative embodiment)    -   2101—diamond (sixth alternative embodiment)    -   2102—backing sheet (sixth alternative embodiment)    -   2200—flat washer section (seventh alternative embodiment)    -   2201—downward-facing teeth (seventh alternative embodiment)    -   2202—tubular body (seventh alternative embodiment)    -   2203—slits (seventh alternative embodiment)    -   2204—outward-facing teeth (seventh alternative embodiment)    -   2600—threaded section (eighth alternative embodiment)    -   2601—tubular body (eighth alternative embodiment)    -   2800—mandrel tail (ninth alternative embodiment)    -   2801—tubular body (ninth alternative embodiment)    -   2802—washer section (ninth alternative embodiment)    -   2803—slits (ninth alternative embodiment)    -   2804—outward-facing teeth (ninth alternative embodiment)    -   2805—downward-facing teeth (ninth alternative embodiment)    -   2900—mandrel head (ninth alternative embodiment)    -   2901—closed tubular end (ninth alternative embodiment)    -   3100—first set of teeth (tenth alternative embodiment)    -   3101—second set of teeth (tenth alternative embodiment)    -   3102—nut (tenth alternative embodiment)    -   3103—clearance hole (tenth alternative embodiment)    -   3104—captive bolt (tenth alternative embodiment)    -   3105—body section (tenth alternative embodiment)    -   3200—first set of teeth (eleventh alternative embodiment)    -   3201—second set of teeth (eleventh alternative embodiment)    -   3202—first metal piece of first solar panel (eleventh        alternative embodiment)    -   3203—second metal piece or second solar panel (eleventh        alternative embodiment)    -   3204—clearance hole (eleventh alternative embodiment)    -   3205—body section (eleventh alternative embodiment)    -   3300—downward-facing teeth (twelfth alternative embodiment)    -   3301—washer section (twelfth alternative embodiment)    -   3400—second metal piece (twelfth alternative embodiment)

DETAILED DESCRIPTION FIGS. 1 Through 5—Preferred Embodiment

FIG. 1 illustrates features of the prior art. This star washer is formedfrom a flat metal piece. Star washer body 100 has two sets of teeth onits internal circumference. FIG. 2 illustrates the prior art in anassembly. The longer teeth 101 will retain the washer on the threads ofscrew 200, the shorter teeth 102 will make electrical connection to theupper metal piece 201 and lower metal piece 202 when the fastener istightened. Teeth 102 are twisted out of the plane of the washer body100. When screw 200 is tightened, upper metal piece 201 and lower metalpiece 202 will press on the teeth 102. Since the washer is made out of aspring metal, teeth 102 will resist the tightening. As screw 200 istightened, teeth 102 will scrape against upper metal piece 200 and lowermetal piece 201. This scraping is sufficient to clear dirt or greasefrom a surface, but is too weak to break through an anodized surface. Asscrew 200 is further tightened, the teeth 102 will be forced back intothe plane of the star washer body 100.

FIG. 2 shows several methods of constructing teeth which areperpendicular to the plane of the washer. As shown in FIGS. 3-6, one maypunch out a single triangular tooth 300 with a triangular punch, or onemay punch out four triangular teeth 400 with a square punch. A largernumber of teeth 500 may be formed with a round shape. To simplify theforming process, a single circular tooth 600 may be made. The circulartooth has the advantage that the resulting structure is very rigid. Itshould be apparent to those skilled in the art that more complex shapescould also be used to form teeth. While punching is probably thesimplest method of forming thin metal pieces into the desired shape, itshould be apparent to those skilled in the art that other methods suchas casting, machining, pressure forming, and photochemical machiningcould be used. The important distinction over the prior art is that theperpendicular orientation of the teeth allows for greater mechanicalcontact and hence greater electrical contact.

As shown in FIG. 7, pins may also be used to obtain the desiredperpendicular structure instead of forming sheet metal. It should beapparent to those skilled in the art that the pins may also be hollow,for instance in a cylindrical shape, or may have an irregular shape.During assembly the opposing pin points will transmit forces directlybetween the two pieces to be connected and so will be the best way toensure that the pins embed into the two pieces. The opposing points alsowill have a short direct path between the pieces to be connected andtherefore have very low resistance; however, this may not be acost-effective method. A more practical method may be to construct apin-like structure as is shown in FIG. 8. Two circular teeth 800 areconstructed on a sheet which is then folded so that the teeth aredirectly opposed. As shown in FIG. 8, the teeth have a cross-sectionalheight greater than their cross-sectional thickness, and, also incross-section, are asymmetrical with respect to the perpendicular.

FIG. 9 shows the preferred embodiment of the invention. The bondingwasher is formed out of a thin metal sheet. Upward-facing teeth 900 areperpendicular to upper washer section 901. Downward-facing teeth 902 areperpendicular to lower washer section 903. The teeth are formed, thenthe part is folded on hinge 904 so that the teeth are in directopposition. The teeth 900 and 902 are shown with a simple smoothcircular shape. It should be evident to those skilled in the art thatmore complicated shapes could also be used. A clearance opening in theform of a hole 905 allows a fastener to be inserted through the bondingwasher. Extending downward on the inner circumference of clearance hole905 are fingers 906.

FIG. 10 shows the preferred embodiment after it has been pushed into ahole 1000 of first metal piece 1001. Fingers 906 are constructed with atwist so that they provide a spring force to retain the bonding washerin position. The preferred embodiment is shown with four fingers. Thisnumber allows the preferred embodiment to provide retention in holes andalso in slots where the slot opening is equal to the distance betweenadjacent fingers. It should be apparent to someone skilled in the artthat other numbers of fingers could also be used.

FIG. 11 shows an exploded assembly with the preferred embodiment. Bolt1100 is inserted through flat washer 1101, second metal piece clearancehole 1103, preferred embodiment clearance hole 905, first metal piece1001, flat washer 1104, split washer 1105 and nut 1106. As nut 1106 istightened, downward-facing teeth 902 will be forced into first metalpiece 1001, upward-facing teeth 900 will be forced into second metalpiece 1102. First metal piece 1001 and second metal piece 1102 arepreferably formed of anodized aluminum. Since the downward-facing teeth902 are perpendicular to the surface of the lower washer section 903 andthe surface of the first metal piece 1001, the teeth cannot spring backbut must embed into the surface of the first metal piece 1001.Similarly, the upward-facing teeth 900 will embed into the surface ofthe second metal piece 1102. The bonding washer is made of a materialharder than that of the first metal piece 1001 and the second metalpiece 1102. The bonding washer may also have a thin coating of amaterial such as chromium or titanium nitride in order to achieve thedesired hardness. Because the upward-facing teeth 900 and thedownward-facing teeth 902 are in close proximity, the electrical pathfrom the first metal piece through the bonding washer to the secondmetal piece is extremely short, and therefore the connection has lowelectrical resistance.

The preferred embodiment is shown with a bolt and nut, but it should beapparent to one skilled in the art that other types of fasteners may beused, including through hole type fasteners such as rivets. Clampingtype fasteners which are positioned outside the first and second metalpieces may also be used.

FIG. 34 shows the embodiment of FIG. 33 as it is assembled with a metalrail.

Height, cross-sectional area, and number of downward-facing teeth andupward-facing teeth can be chosen in order to achieve a desired value ofelectrical conductivity. These choices must be traded off against theclamping force required to force the pieces together.

Alternative Embodiments—FIGS. 12-33

FIGS. 12 and 13 show two views of an alternative embodiment of theinvention, a U-shaped metal sheet featuring upward-facing teeth 1200 anddownward-facing teeth 1301, perpendicular to body 1201, and anelliptical clearance opening 1202. The end of each arm of the “U” iscurved into a perpendicular U-shaped bend 1203, ending in tab 1204,which forms a spring clip.

FIG. 14 shows this alternative embodiment, pushed onto the edge ofsecond metal piece 1102. The spring clip formed by U-shaped bend 1203and tab 1204 attaches the bonding washer to the second metal piece 1102.Tab 1204 is constructed to be outside the diameter of flat washer 1101so that flat washer 1101 can provide even force against second metalpiece 1102. Clearance opening 1202 allows a fastener to be insertedthrough the bonding washer. Clearance opening 1202 is somewhatelliptical in shape in order to accommodate variability in the positionof hole 1103.

FIG. 15 shows a second alternative embodiment of the invention, a clipformed by a pair of parallel U-shaped plates joined by two U-shapedbends and having a first set of upward-facing teeth 1500 on first bodysection 1501 and a second set of upward-facing teeth 1502 on second bodysection 1503. When the clip is mounted on a metal piece, the second setof upward-facing teeth 1502 will contact that metal piece. Afterassembly, the first set of upward-facing teeth 1500 will contact asecond metal piece. By using two body sections, more teeth can beaccommodated and in general this will result in reduced electricalresistance through the teeth. The electrical path from the first metalpiece through the clip to the second metal piece is now longer than forthe first alternative embodiment, so that portion of the electricalresistance will be greater. Depending on the exact details ofconstruction the total electrical resistance may be greater or less thanfor the first alternative embodiment.

A variation of this embodiment would allow the clip to be pushed onafter first metal piece 1001 and second metal piece 1102 have beenpositioned together. In that case, the teeth would be made to contactboth pieces from the outside.

FIG. 16 shows a third alternative embodiment of the invention, whichtakes the form of a clamp with two vertical sides, comprising springfingers 1602, perpendicular to a flat rectangular surface 1603 bearingupward-facing teeth 1600 and downward-facing teeth 1601. FIG. 17 showshow the spring fingers grab on to the sides 1701 and 1702 of a metalrail 1700. The spring fingers retain the clamp in place on metal rail1700 while it is assembled into a larger structure. The fastener for thethird alternative embodiment will generally be of the clamping type foruse in applications where clamping is appropriate, as opposed to boltingthrough a clearance hole.

FIGS. 18 and 19 show a fourth alternative embodiment of the inventionand its application, respectively. A circular washer bears upward-facingteeth 1801. Downward contacting teeth 1800 are perpendicular to tubularsection 1802. The outer diameter of the downward contacting teeth 1800is chosen so that it can be press fit into first metal piece 1001. Atool is required which can exert sufficient pressure on flat portion1803 in order to force the bonding washer into hole 1000, deforming thematerial of first metal piece 1001 around hole 1000. As a result of thispress-fit operation, the bonding washer is firmly mechanically andelectrically joined to first metal piece 1001, as shown in FIG. 19. Thefirst metal piece 1001 may now be mechanically assembled into a largerstructure, such that teeth 1801 will embed in the metal of the largerstructure.

FIG. 20 shows a fifth alternative embodiment of the invention. Flatwasher-like section 2000 has embedded pins 2001. The pins 2001 arepointed at both ends and so will embed into the two metal pieces duringassembly to make electrical contact. Since conduction is only throughthe pins, flat washer-like section 2000 may be made of plastic.Retention feature 2002, a short cylinder attached to the washer-likesection, is also made of plastic and so may readily deform when pressedinto a hole. The plastic should be chosen to provide a spring actionwhich retains the washer in the hole.

FIG. 21 shows a sixth alternative embodiment of the invention.Double-sided adhesive sheet 2100 has small industrial diamonds 2101stuck to one side. The sheet 2100 may be peeled off backing sheet 2102,exposing adhesive on its underside. Sheet 2100 may then be stuck to ametal piece, the adhesive retaining the washer and diamonds in position.The force applied during assembly will cause the diamonds to penetratethe adhesive. The irregular shape of the diamonds will allow them tofunction like the pins of the fifth alternative embodiment directlyconducting current from one metal piece to the other.

FIGS. 22 and 23 show a seventh alternative embodiment of the invention,in isolation and aligned with pieces to be attached, respectively. Oneend has a flat washer section 2200, bearing downward-facing teeth 2201,which function identically to those of the preferred embodiment. Tubularbody 2202 has slits 2203 which begin a distance from washer section 2200sufficient to accommodate the combined thickness of first metal piece1001 and second metal piece 1102. The surfaces between slits 2203 haveoutward facing teeth 2204 along the first half of their length.

The seventh alternative embodiment does not have retention features.When first metal piece 1001 and second metal piece 1102 are aligned,bolt 1100 is inserted through the bonding washer unit, then bolt 1100and the bonding washer unit together are inserted through second metalpiece 1102 and first metal piece 1001. As in FIG. 4, washer 1104, splitwasher 1105, and nut 1106 are installed on bolt 1100. When nut 1106 istightened, elements illustrated in FIG. 22 collapse, as tubular body2202 folds back on itself in the vicinity of the slits 2203. (FIGS. 24and 25 show how the outward-facing teeth 2204 will then face towardfirst metal piece 1001.) As nut 1106 is further tightened,downward-facing teeth 2201 embed into second metal piece 1102 andoutward-facing teeth 2204 embed into first metal piece 1001, thuselectrically connecting first metal piece 1001 and second metal piece1102. Installation of the seventh alternative embodiment entails alonger electrical path between the first metal piece 1001 and secondmetal piece 1102 than the preferred embodiment and is therefore lessdesirable. It may, however, represent some cost savings in the assemblyprocess.

FIG. 26 shows a eighth alternative embodiment similar to the seventhalternative embodiment, except that nut 1106 has been replaced by athreaded section 2600 within tubular section 2601. As shown in FIG. 27,when bolt 1100 is inserted into the threaded section and tightened, itpresses against washer 1101 and deforms the bonding washer unit, makingelectrical connection in a similar fashion as with the seventhalternative embodiment.

FIGS. 28 and 29 show a ninth alternative embodiment similar to theseventh alternative embodiment but incorporating rivet features. Mandrelhead 2900 is engaged with closed tubular end 2901. Mandrel tail 2800protrudes through tubular body 2801 and out past washer section 2802.Assembly is illustrated in FIG. 30. The holes of two metal pieces 1001and 1102 are aligned, and the bonding washer unit is inserted throughboth holes. A riveting tool is used to push down on washer section 2802while pulling on mandrel tail 2800. The pulling force will cause tubularbody 2801 to deform in the vicinity of slits 2803. Outward-facing teeth2804 will move until they face toward first metal piece 1001, in asimilar manner as shown in FIGS. 24 and 25. As additional pulling forceis exerted on mandrel tail 2800, downward-facing teeth 2805 embed intosecond metal piece 1102, and outward-facing teeth 2804 embed into firstmetal piece 1001, thus electrically connecting the two metal pieces. Theninth alternative embodiment has a longer electrical path between thefirst metal piece 1001 and second metal piece 1102 than the preferredembodiment and therefore has greater resistance. It may, however,represent some cost savings from the assembly process.

As with normal rivets, the pulling force results in a deformation ofmandrel head 2900 and closed tubular end 2901 which mechanically holdsthe entire assembly in place. As the pulling force is further increased,mandrel tail 2800 breaks off for a finished assembly.

FIG. 31 shows a tenth alternative implementation of the invention. Thisimplementation incorporates a clamping function appropriate for use witha solar module and mounting rail. In use, second metal piece 1102 ofsolar module is positioned on metal rail 1700. First set of teeth 3100are then positioned to contact metal rail 1700: second set of teeth 3101are positioned to contact second metal piece 1102. Captive bolt 3104 isinserted through hole 3103 and screwed into nut 3102. As captive bolt3104 is tightened against body section 3105, first set of teeth 3100embed into metal rail 1700 and second set of teeth 3101 embed intosecond metal piece 1102, thus making electrical connection. Captive bolt3104 is further tightened to provide sufficient clamping force betweenfirst metal piece 1001 and second metal piece 1102. This implementationmay be fabricated with sheet metal or machined from an extruded blank.It should be apparent to someone skilled in the art that otherfabrication techniques may also be used.

FIG. 32 shows an eleventh alternative implementation of the invention.This implementation incorporates a clamping function appropriate for usewith two solar modules and a mounting rail. In use, first set of teeth3200 are positioned to contact first metal piece 3202 of first solarmodule. Second set of teeth 3201 are positioned to contact second metalpiece 3203 of second solar module. Bolt 3104 is captive in mounting rail3205. Bolt 3104 is inserted through hole 3204 and screwed into nut 3102.As nut 3102 is tightened against body section 3205, first set of teeth3200 embed into first metal piece 3202 and second set of teeth 3201embed into second metal piece 3203, thus making electrical connectionbetween the two solar modules. Nut 3102 is further tightened to providesufficient clamping force between first metal piece 3202, second metalpiece 3204 and metal rail 1700.

FIG. 33 shows a twelfth alternative implementation of the invention.This implementation is appropriate for use when only one of the metalpieces has an anodized coating. The bonding washer consists of a bodysection 3301 and one set of downward facing teeth 3300. FIG. 34 showsthe twelfth alternative embodiment as it is assembled. Downward facingteeth 3300 are positioned to contact metal rail 1700. Second metal piece3400 directly contacts washer section 3301. Second metal piece 3400 isconstructed of a corrosion resistant material such as tin plated copper,zinc coated steel, or stainless steel. It should be apparent to someoneskilled in the art that other suitable materials may be used. Thebonding washer is also constructed out of a corrosion resistant materialand therefore good electrical connection can be made just by clampingthe two pieces together. As bolt 1100 and nut 1106 are tightened,downward facing teeth 3300 will forcibly embed themselves into metalrail 1700, thereby making electrical contact.

CONCLUSIONS, RAMIFICATIONS, AND SCOPE OF INVENTION

Thus the reader will see that the bonding washer of the inventionprovides a fastener which offers excellent electrical bonding of metalpieces used in photovoltaic and other applications. The alternativeembodiments described herein make the bonding washer design adaptable toa wide range of situations, while promoting ease of assembly.

Although the description above contains many specificities, these shouldnot be construed as limiting the scope of the invention but as merelyproviding illustrations of some of the presently preferred embodimentsof this invention. Thus the scope of the invention should be determinedby the appended claims and their legal equivalents, rather than by theexamples given.

What is claimed is:
 1. A bonding element for making an electricalconnection between two metal pieces when the metal pieces are rigidlyclamped together with at least a portion of the bonding element disposedbetween them, the bonding element comprising a sheet metal body member,which comprises: a first body portion and a second body portion, saidbody portions folded together so as to be contiguous; a first set ofteeth, numbering one or more, formed on said first body portion andextending away from said body member in a first direction substantiallyperpendicular to said first and second body portions, each tooth of saidfirst set having a distal edge; and a second set of teeth, numbering oneor more, formed on said second body portion and extending away from saidbody member in a second direction substantially opposite said firstdirection, each tooth of said second set having a distal edge, whereinat least one tooth of said second set of teeth is substantially alignedwith a tooth of said first set of teeth to define at least one pair ofsubstantially aligned, diverging teeth, whereby, when the metal piecesare clamped together with said first and second sets of teeth betweenthem, the distal edges of said teeth are forcibly embedded into themetal pieces to make electrical contact therewith.
 2. The bondingelement of claim 1, wherein the distal edge of each tooth issubstantially smooth.
 3. The bonding element of claim 2, wherein thedistal edge of each tooth is substantially circular.
 4. The bondingelement of claim 1, wherein the distal edge of each tooth issubstantially circular.
 5. The bonding element of claim 1, wherein eachpair of substantially aligned teeth are hollow.
 6. The bonding elementof claim 5, wherein each pair of substantially aligned teeth define ahole through the body member.
 7. The bonding element of claim 1, whereinsaid first and second sets of teeth comprise plural pairs ofsubstantially aligned, diverging teeth.
 8. A bonding washer for makingan electrical connection between two metal pieces when the metal piecesare rigidly held together by a fastener with at least a portion of thebonding washer disposed between them, the bonding washer comprising asheet metal body member, which comprises: first and second substantiallycongruent body portions folded together about a hinge portion so as tobe contiguous and substantially coextensive; an opening in each of saidbody portions through which a fastener can extend, said openings beingsubstantially coextensive and substantially aligned; a first set ofteeth formed on said first body portion and extending away from saidbody member in a first direction substantially perpendicular to saidfirst and second body portions, each tooth of said first set of teethhaving a distal edge; and a second set of teeth formed on said secondbody portion and extending away from said body member in a seconddirection substantially opposite said first direction, each tooth ofsaid second set of teeth having a distal edge and being substantiallyaligned with a respective tooth of said first set of teeth to definepairs of substantially aligned, diverging teeth, whereby, when afastener extending through said openings is tightened with said firstand second sets of teeth between the metal pieces, the distal edges ofsaid teeth are forcibly embedded into the metal pieces to makeelectrical contact therewith.
 9. The bonding washer of claim 8, whereineach of said openings comprises a hole located substantially at thecenter of its respective body portion, and said teeth surround saidholes.
 10. The bonding washer of claim 9, wherein said body portions aresubstantially annular.
 11. The bonding washer of claim 10, wherein thedistal edge of each tooth is substantially circular.
 12. The bondingwasher of claim 11, wherein the distal edge of each tooth issubstantially smooth.
 13. The bonding washer of claim 12, wherein eachpair of substantially aligned teeth are hollow.
 14. The bonding washerof claim 13, wherein each pair of substantially aligned teeth define ahole through the body member.
 15. The bonding washer of claim 8, whereinthe distal edge of each tooth is substantially circular and smooth. 16.The bonding washer of claim 15, wherein each pair of substantiallyaligned teeth define a hole through the body member.
 17. A bondingelement for making an electrical connection between two metal pieceswhen the metal pieces are rigidly clamped together with at least aportion of the bonding element disposed between them, the bondingelement comprising: a metal body having a first face and a second face,said first and second faces facing away from said body in oppositedirections; a first set of teeth, numbering one or more, formed on saidbody and extending outwardly away from said first face substantiallyperpendicular to a plane of said body, each tooth of said first sethaving a distal edge; and a second set of teeth, numbering one or more,formed on said body and extending outwardly away from said second facesubstantially perpendicular to said plane of said body, each tooth ofsaid second set having a distal edge, wherein at least one tooth of saidsecond set of teeth is substantially aligned with a tooth of said firstset of teeth to define at least one pair of substantially aligned,diverging teeth, each tooth of said pair of substantially aligned teethhaving a substantially annular distal edge and a hollow interior,whereby, when the metal pieces are clamped together with said first andsecond sets of teeth between them, the distal edges of said teeth areforcibly embedded into the metal pieces to make electrical contacttherewith.
 18. The bonding element of claim 17, wherein the distal edgeof each tooth of each substantially aligned pair of teeth issubstantially smooth.
 19. The bonding element of claim 18, wherein eachpair of aligned teeth define a hole through said body.
 20. The bondingelement of claim 19, wherein all of said teeth are substantiallyuniform.